In known LED encapsulating materials, the thermal conductivity of the material is too often low to obtain an effective cooling of the LED is not provided. Materials, which provide an effective cooling of the LED, are in general not flexible enough for obtaining a flexible lighting assembly which may be provided to a curved profile. Another set of known materials comprises electrically conductive particles for enhancing the thermal conductivity, however, such electrically conductive particles have the risk of causing short-circuits between the wires which provide power to the LED.
Published patent application U.S. 2009/0273925 discloses a LED illumination assembly with a compliant foil construction. The assembly comprises Light Emitting Diodes (LEDs) which are provided on a stack of layers. In this paragraph it is assumed that the layer on which the LEDs are provided is defined as the top layer of the stack of layers. The top layer comprises metal wires, which provide, for example, power to the LEDs. Directly below the top layer is provided a polymeric layer which comprises particles for enhancing the thermal conductivity of the polymeric layer. A disclosed example of the particles is boron nitride. Preferably the polymeric layer is electrically insulating and has a relatively good thermal conductivity to provide heat generated by the LEDs to other layers below the polymeric layer. In specific embodiments the LEDs are in direct contact with the metal wires via which the heat of the LED is provided to the polymeric layer. In other embodiments a specific surface of the LEDs is also in contact with the polymeric layer.
Although the polymeric layer with boron nitride particles provides to some degree a cooling effect to the LED, the polymeric layer does not provide the thermal characteristics which are required to have an effective cooling of the LED. For, example, in a flexible lighting assembly in which LEDs and power wires of the LEDs are (partly) encapsulated, better thermal characteristics are desired to prevent to prevent too high LED temperatures.